Vocabulary: Element Builder Vocabulary Atom – the basic unit of matter. o An atom is the smallest particle of an element that still has all the properties of the element. o Atoms are made up of smaller particles called protons, neutrons, and electrons. The smaller electrons orbit around a central nucleus of protons and neutrons. Atomic number – the number of protons in the nucleus of an atom. o Elements are distinguished from one another by their atomic numbers. o For example, any atom with two protons is an atom of helium. o The symbol for the atomic number is Z. o In an element symbol, the atomic number is shown at lower left. Electron – a negatively charged particle that moves around the nucleus. o Electron dot diagram – a diagram that shows the element symbol surrounded by dots representing valence electrons. o The mass of an electron is less than one thousandth of the mass of a proton. For example, the electron dot diagram at right shows that neutral helium atoms have two valence electrons. Element – a pure substance that cannot be broken down into simpler substances by ordinary chemical means. o Elements are made of one type of atom. o Atoms of different elements are distinguished by the number of protons in the nucleus. For example, all carbon atoms have 6 protons. Energy level – a particular region where electrons can orbit a nucleus. Ion – an atom or molecule that has an electrical charge because it has gained or lost electrons. o An atom with more protons than electrons is a positively charged ion, or cation. o An atom with more electrons than protons is a negatively charged ion, or anion. o In an element symbol, the electric charge is shown at upper right. Isotope – one of several forms of the same element. o All isotopes of a given element have the same number of protons, but differ in the number of neutrons. o Most isotopes are radioactive. Usually only one or two stable isotopes exist for a given element. Mass number – the number of protons plus neutrons in the nucleus of an atom. o For example, the mass number of helium is 4 (2 protons and 2 neutrons). o The symbol for the mass number is A. o In an element symbol, the mass number is shown at upper left. Neutron – a particle with no charge located in the nucleus of an atom. o Neutrons have slightly more mass than protons. o The number of neutrons is described by the neutron number, N. o To find the number of neutrons, subtract the atomic number from the mass number. Nucleus – the positively charged, dense center of an atom. o The nucleus contains protons and neutrons. Periodic table – a chart that organizes the chemical elements based on their properties. Proton – a positively charged particle located in the nucleus of an atom. o Protons have slightly less mass than neutrons. o The number of protons determines the element. Radioactive – capable of releasing radiation. o In a radioactive atom, the nucleus can spontaneously decay and emit particles and/or light. These emissions are called radiation. o The energy released by radioactive substances can be harnessed to produce electricity in a nuclear power plant. This energy also can be used to create a massive explosion in a nuclear bomb. o If the emissions change the number of protons in the nucleus, the atom becomes a different element. Valence electrons – electrons found in the outermost energy level of an atom.